The invention relates to a method for operating an internal combustion engine especially of a motor vehicle, wherein fuel is injected into a combustion chamber in at least two modes of operation. The injection includes an injection start angle and an injection duration. Likewise, the invention relates to an internal combustion engine, especially for a motor vehicle, having a combustion chamber into which fuel can be injected in at least two modes of operation. The injection includes an injection start angle and an injection duration. The internal combustion engine includes a control apparatus for control (open loop and/or closed loop).
A method of this kind and an internal combustion engine of this kind are known, for example, from a so-called gasoline direct injection in motor vehicles. There, fuel is injected into the combustion chamber of the engine in a homogeneous operation during the induction phase or, in a stratified operation, during the compression phase. The homogeneous operation is preferably provided for the full-load operation of the engine; whereas, the stratified operation is suitable for idle operation or part-load operation. In such a direct-injecting internal combustion engine, there is a switchover between the two above-mentioned operating modes, for example, in dependence upon the requested torque.
The starting of the engine is carried out in homogeneous operation. Especially for a cold start, it is possible that a relatively long injection duration is required because of the pressure which is still low and operates on the fuel, in order to be able to inject the wanted fuel mass into the combustion chamber and to start the engine reliably. This can lead to the situation that the engine transfers already from the induction phase into the compression phase and that the pressure, which develops thereupon in the combustion chamber, is greater than the pressure operating on the fuel. In this case, the fuel and vapor from the combustion chamber would be blown back which, in any case, should be avoided.
It is an object of the invention to provide a method for operating an internal combustion engine with which a reliable start can be carried out, even a cold start.
This task is solved in accordance with the invention by a method of the above-mentioned type in that an injection end angle is determined from the injection start angle and the injection duration and that a check is made as to whether an injection interrupt angle is exceeded by the injection end angle. For an internal combustion engine of the kind referred to above, the task of the invention is solved in that an injection end angle can be determined by the control apparatus from the injection start angle and the injection duration and that a check can be made by the control apparatus as to whether an injection interrupt angle is exceeded by the injection end angle.
With the determination of the injection end angle, it is possible that this angle be compared to the injection interrupt angle. From this comparison, it can be derived as to whether the intended injection would or would not exceed the injection interrupt angle. It can then be decided in dependence thereon as to whether any measures are required as to how the intended fuel mass can be injected into the combustion chamber without fuel and vapor being blown back from the combustion chamber.
The invention thereby opens the possibility to inject the wanted fuel mass and to nonetheless avoid a blowback of the fuel. The procedure of the invention can be applied under all operating conditions of the engine and therefore also for a cold start. In this way, a reliable starting of the engine under all conditions is achieved with the invention.
At this point, it is emphasized that each of the above-mentioned angles as well as each of the angles described hereinafter is assigned a corresponding time duration. All angles could therefore be replaced by corresponding time durations. The conversion is dependent upon the rpm of the engine.
In the event that the injection interrupt angle is not exceeded, it is especially advantageous in the invention when the injection is begun at the injection start angle. In this case, which does not include the danger of a blowback of the fuel from the combustion chamber, the injection start angle is therefore not changed. The intended fuel mass is therefore injected into the combustion chamber ahead of the injection interrupt angle.
If, in contrast, the injection interrupt angle is exceeded, then, in an especially advantageous embodiment of the invention, it is provided that a changed injection start angle is so determined that the injection interrupt angle is just no longer exceeded and that the injection is started at the changed injection start angle. In this way, it is ensured that, for an approximately constant rpm, the injection in no case exceeds the injection interrupt angle. In this way, on the one hand, a blowback of fuel from the combustion chamber is reliably avoided. On the other hand, it is likewise avoided that the injection of fuel ends prematurely and that thereby too little fuel is injected into the combustion chamber. Especially the latter is essential for a reliable starting of the engine.
In an advantageous further embodiment of the invention, the injection start angle is changed to xe2x80x9cearlyxe2x80x9d. It is especially advantageous when the injection start angle is changed starting from the injection interrupt angle toward xe2x80x9cearlyxe2x80x9d by the injection duration. According to the invention, the injection is therefore started precisely when the remaining time duration up to the interruption of the injection just corresponds to the injection duration. The injection is then precisely at the time point of the provided interrupt or is ended at the injection interrupt angle.
In a further advantageous embodiment of the invention, the change of the injection start angle is limited to a limit angle which is especially engine temperature dependent. In this way, it is achieved that the injection start cannot be changed arbitrarily to xe2x80x9cearlyxe2x80x9d; instead, an earliest possible injection start in each case is maintained.
The application of the invention is especially advantageous in a first operating mode wherein the fuel is injected into the combustion chamber of the engine during the induction phase. This operating mode defines the homogeneous operation.
Likewise, it is especially advantageous when the invention is used at a pressure, which acts on the fuel, which is less than a limit pressure. In this way, it can be achieved that a change of the injection start angle is only possible when the pressure, which acts on the fuel, is low and therefore, for an interrupt, too little fuel would be injected for a reliable operation of the engine. For a high pressure acting on the fuel, the injection times are so short that no interruption can occur any longer. The entire computations are no longer carried out in order to save computation time.
An especially advantageous embodiment of the invention is applying the same during start of the engine. When starting, especially for a cold start, the pressure on the fuel is low. At the same time, a large quantity of fuel must be injected into the combustion chamber in order to ensure a reliable starting of the engine. An interruption of the injection during starting could therefore lead to a stalling of the engine. For this reason, it is especially advantageous to prevent an interruption of the injection during starting of the engine and, in lieu thereof, carry out the change of the injection start angle in accordance with the invention. In this way, it is, on the one hand, achieved that the intended fuel mass can be completely injected into the combustion chamber. On the other hand, a blowback of fuel out of the combustion chamber is reliably avoided.
Of special significance is the realization of the method of the invention in the form of a control element which is provided for a control apparatus of an engine, especially of a motor vehicle. A program is stored on the control element which is capable of being run on a computer, especially on a microprocessor, and is suitable for executing the method according to the invention. In this case, the invention is realized by a program stored on the control element so that this control element, which is provided with the program, defines the invention in the same way as the method which the program can carry out. Especially an electric storage medium can be used as a control element, for example, a read-only-memory or a flash memory.
Further features, application possibilities and advantages of the invention will become apparent from the following description of embodiments of the invention which are illustrated in the drawing. All described or illustrated features define the subject matter of the invention by themselves or in any desired combination independently of their summary in the patent claims or their dependency as well as independently of their formulation or presentation in the description and/or in the drawing.